Phosphoinositide phosphates (PlPns) are important second messengers in signaling pathways controlling cellular proliferation, survival, morphology, and motility. Disruption of these pathways is common to many disease states, including diabetes, cardiovascular disease, and cancer. Because the activity of lipid second messengers is often determined by their phosphorylation state, the enzymes that act to modify these lipids are central to the correct execution of many signaling events. We propose to develop novel methods for the determination of phosphoinositide phosphatase activity. These assays will be aimed at measuring the activity of the lipid phosphatases PTEN, SHIP1, and SHIP2, which modulate phosphoinositide 3-kinase signaling by conversion of Pl (3,4,5) P3 to Pl (4,5) P2 and Pl(3,4)P2 respectively. These enzymes are important in signaling pathways that regulate insulin sensitivity and allergic and immune response, and which are often altered in carcinogenesis. Because signaling events involving these phsophoinositide phosphatases are often perturbed in disease progression, particularly non-insulin dependent diabetes mellitus (NIDDM) and cancer, these assays should have significant value as research and diagnostic tools as well as drug-screening platforms.